Ex-Mets first baseman and SNY analyst Keith Hernandez can lead a team to a championship without batting a eyelash (or a mustache).

But saying lines on "Seinfeld," one of the most iconic sitcoms in television history? Much more nerve-wracking, it turns out.

Hernandez spoke to "Rolling Stone" about how he got his role on the show. It started -- like much of modern baseball history -- with his agent, Scott Boras. Hernandez didn't want to be an actor, but he found out the pay and was told he would be flown to Los Angeles and would have just "a few lines."

"They FedExed me the script, and I saw I had lots of lines," he remembered. "I thought 'Holy [expletive], I'm can't do this!' So I kind of got a head start on it, because I was mortified. I memorized everybody's lines in every scene I was in. I knew when they were going to speak, when it was my turn, all that. I was really nervous before we shot in front of the live audience, and Jerry turns to me and went 'What the hell are you nervous for? You play in front of 50,000 people.' And I said 'Well, I don’t have to memorize lines when I'm playing in front of them.'"

The episode Hernandez was in -- "The Boyfriend" -- turned out to have two parts and ran during sweeps. But if Hernandez was terrible, executive producer told Hernandez there was an extra plot written in: George Costanza's battle with the unemployment benefits (remember "Vandelay Industries"?).

"So, with those scenes, it turned into an hour-long show," he said. "If I was bad, it was only going to be a half-hour."